Amblyopia and associated deficits in binocular function are estimated to affect 2% of the American population. Recent studies of visual development in animal models suggest that many of these deficits are direct results of abnormal visual experience during early postnatal months and, therefore may be preventable or reversible with appropriate early intervention. During the previous grant period, preferential- looking, operant, and visually evoked potential techniques were used to study the normal course of human visual development and visual development of infants with binocular imbalance. Continued prospective follow-up of approximately 200 infants with infantile esotropia or unilateral cataract, enrolled during the first 4 years of the grant, will provide sensory and alignment outcome data at 5- 9 years of age. These data will clarify the relative efficacy and effectiveness of treatment regimens for early binocular imbalance. New prospective studies will evaluate the prognostic value of preferential- looking acuity for success of occlusion therapy and for outcome following surgery for infantile unilateral cataract. Combined measures of preferential-looking and visually evoked potential stereoacuity and fusion will examine developing central and peripheral binocular deficits in infantile esotropia. Prospective monocular vernier acuity measurement will provide a sensitive new index of developing spatial deficits and of response to treatment. A modified paradigm for binocular luminance summation in the pupil response will be used to measure central suppression in pre-verbal patients. Infants with delayed visual maturation may or may not suffer long-term visual impairment. Early identification of those with a poor prognosis is important because they are at high risk for neurological sequelae, and for rehabilitation efforts, genetic counseling, and social services. Prospective evaluation of preferential-looking and visually evoked potential acuity in this population should define an optimum protocol for infants with delayed visual maturation.